Generally, in a power converter unit, in order to reduce the influence of malfunction caused by the noise accompanied on wirings, a drive circuit for driving power semiconductor devices is mounted near the power semiconductor devices. Since the power semiconductor device generate a lot of heat by switching operation, the drive circuit tends to be affected by the heat generated by the power semiconductor devices. Further, in recent years, there is a tendency for the environmental temperature of power converter units to be higher. Therefore, countermeasures, such as raising maximum allowable temperatures of parts mounted on the drive circuit, are required.
If trying to raise the maximum allowable temperatures of drive circuit parts, a cost of the parts to be used will be higher, and reliability will be lowered. A structure for solving the above problem is disclosed in Japanese Patent Laid-open No. 2004-282804 (Patent document 1). In the disclosure, a drive circuit is arranged right above the power semiconductor devices. A drive circuit board on which the drive circuit is mounted is connected to a first heat dissipating plate by using an adhesive. The heat dissipating plate is contacted with a second heat dissipating plate to be fixed to a cooler of the power semiconductor device. Thus, the heat of the drive circuit is reduced by directing the heat of the drive circuit to the cooler through the highly heat dissipating plates.    Patent document 1: Japanese Patent Laid-open No. 2004-282804
However, in the above structure, in order to connect the drive circuit board with the heat dissipating plate, it is necessary to use an adhesive. Therefore, there are required time consuming processes such as a curing time for the adhesive. Also, the drive circuit board is fixed to the heat dissipating plate side. Therefore, it is necessary to carry out wiring between the drive circuit board and the power semiconductor device by using an additional member, such as a flexible substrate etc., making the assembly difficult. Further, the drive circuit board is mounted right above the power semiconductor devices. Therefore, the drive circuit board on the drive circuit is easily be influenced by the switching noise of the power semiconductor device, causing a problem in noise immunity.